1. Field of the Invention
The present invention is directed to a HF surgery device, and in particular to a HF surgery device which includes a microprocessor-controlled circuit to maintain the HF output signal at a constant output power.
2. Description of the Prior Art
HF surgery devices are known in the art which include a microprocessor and a comparator for acting in combination to generate a control signal, the control signal acting on a rectified operating voltage to control the HF output signal. Such a surgery device is disclosed in European application 0 316 469. The HF output signal in this known device can be modulated with a modulation signal. Also in this known surgery device, various reference values for the HF voltage can be supplied to the comparison circuit. The reference values can be pre-programmed, and contained within the microprocessor, and can be selected by an actuating switch, for example, at an electrode handle. The required comparison signal is formed from the HF output voltage, for which purpose an insulating component, for example a transformer, and at least one voltage converter are required. The HF output signal must have a constant level, which is is the case in the event of an amplitude modulation. In this known HF surgery device, a check must be undertaken to determine whether the comparison signal is to be proportional to the peak value, to the effective value, or to an average value of the modulated HF output voltage. Therefore, additional voltage converters are required, which must be activated by the operator as needed.
In order to achieve a deep coagulation, the ratio of the peak voltage to the effective voltage is increased by the modulation, but the effective output power must remain substantially constant. Power increases or decreases arise in the HF output voltage due to the amplitude modulation, the increase or decrease arising in accord with the envelope of the modulation signal. The HF output voltage therefore does not have a constant level in this known apparatus. Consequently, a significant decrease in the available, effective output power occurs due to the valleys in the shape of the output voltage signal which occur, for example, in the event of regulation dependent on the peak value of the HF output voltage. A satisfactory coagulation is thus not possible.
The operator of this known HF surgery device must therefore compensate power drops caused by the modulation by switching to a different voltage converter and to a higher output voltage. There may, however, be difficulties related to such switching insofar as a non-linear relationship exists between the operating voltage an the HF output power. A less skillful operator of the HF surgery device can be easily overburdened with this selection and setting of the suitable parameters.